1. Field of the Invention
This invention relates to human immunodeficiency virus (hereinafter “HIV”) gp41 C-terminal peptide derivatives that are inhibitors of viral infection and/or exhibit antifusogenic properties. In particular, this invention relates to peptide derivatives having inhibiting activity against HIV and simian immunodeficiency virus (hereinafter “SIV”), with improved solubility and extended duration of action for the treatment of the respective viral infections.
2. Review of Related Art
Membrane fusion events are commonplace in normal cell biological processes, and membrane fusion is also involved in a variety of disease states, including, for example the entry of enveloped viruses into cells. Some enveloped viruses fuse with target cells by specific binding reactions between proteins of the virus envelop and cell surface proteins which trigger conformational changes in associated viral proteins that in turn promote fusion of the viral envelop with the cell membrane.
One enveloped virus, HIV, is a member of the lentivirus family of retroviruses, and there are two prevalent types of HIV, HIV-1 and HIV-2, with various strains of each having been identified. The fusion of HIV and its host cells is mediated by the binding of viral envelop proteins gp120 and gp41, with the CD4 glycoprotein and a chemokine co-receptor on the cell surface. Binding of gp120 to CD4 on the surface of T cells and to a co-receptor (e.g., CCR5 or CXCR4) is followed by insertion of gp41 into the membrane of the target cell; then helicies from the N-terminal portion of gp41 form coiled coil structures with helicies from the C-terminal portion of the same protein, which draws the virus and the cell together for fusion (Malashkevich, et al., Proc. Natl. Acad. Sci. USA, 1998 Aug. 4; 95(16):9134-9).
Peptides are known to inhibit or otherwise disrupt membrane fusion-associated events, including, for example, inhibiting retroviral transmission to uninfected cells. Peptides from the second heptad repeat region of HIV envelop protein gp41, including T20 (DP178) and C34, have shown potent anti-viral activity against HIV in vitro (see Wild, et al., 1994, Proc. Natl. Acad. Sci. USA, 91:9770-4; Chan, et al., 1998, Proc. Natl. Acad. Sci. USA, 95:15613-15617). The demonstrated anti-viral activity includes inhibiting CD4+ cell infection by free virus and/or inhibiting HIV-induced syncytia formation between infected and uninfected CD4+ cells. The inhibition is believed to occur by binding of these peptides to the first heptad repeat region in gp41, thus preventing the first and second heptad repeat regions from forming the fusogenic hairpin structure.
While many of the anti-viral or anti-fusogenic peptides described in the art exhibit potent anti-viral and/or anti-fusogenic activity in vitro, they suffer from short half-life in vivo, primarily due to rapid serum clearance and peptidase and protease activity. This in turn greatly reduces their effective anti-viral activity. There is therefore a need for a method of prolonging the half-life of peptides in vivo without substantially affecting the anti-fusogenic activity.
One method for prolonging the half-life of peptides is disclosed in U.S. Pat. No. 5,612,034, which describes a method for covalently coupling a therapeutic peptide to a native protein found in the blood stream. The peptide is modified with a chemically reactive moiety that is capable of reacting with fuctionalities present on proteins in the blood stream. Upon injection of the modified peptide into the blood stream, it is linked to a long-lived blood component forming a long-lived depot of the peptide. However, since the molecular weight of proteins in the blood stream ranges between 50-600 kD, there is concern that the biological activity of such linked peptides may be compromised by steric hinderance of the much larger size protein.
An attempt to prolong the half-life of a known anti-fusogenic peptide is disclosed in International Patent Publication WO 00/69902 (hereinafter “the '902 publication”) by Conjuchem, Inc. In this disclosure, DP178 is modified by attaching 3-maleimidopropionic acid by an amide link to the epsilon amino group of lysine which is in turn linked by peptide bond to the C-terminal Phe of DP178. The '902 publication also proposes analogs of the modified DP178 which are either truncations of DP178 or corresponding fragments of gp41 from other HIV viral isolates. The '902 publication does not suggest any other design criteria for anti-fusogenic peptides.
Therefore, there remains a need for a method of prolonging the half-life of peptides in vivo without substantially affecting the anti-fusogenic activity.